Several organohalide compounds are metabolized to reactive intermediates presumed to be the ultimately toxic molecules. The reactive metabolites are detoxified by reacting with tissue non-protein sulfhydryls (NPS), and acute toxicity occurs only when NPS have been depleted below a critical level. Upon prolonged chemical exposure, however, a dynamic state exists between chemical metabolism, NPS depletion, NPS synthesis, and lesion development. Whether or not the same relationship exists between tissue NPS concentrations and the development of lesions in a chronic exposure situation as in an acute one is being evaluated. Also, the organ-specificity and species-specificity of these phenomena are being studied.